Electrodes are known that have a configuration in which a material capable of releasing a chemical species that functions as a charge carrier is held by a power collector. An example of this type of electrode is an electrode for a secondary battery having a configuration in which a material (active material) capable of reversibly occluding and releasing the chemical species is held by a metallic power collector. This electrode can be used as a positive electrode or negative electrode that composes a lithium ion battery in which an electrolyte (typically a non-aqueous electrolyte), interposed between the positive electrode or negative electrode and a counter-electrode, is charged and discharged by the migration of lithium ions. A typical example of a method for holding the active material on the power collector is a method in which a paste-like or slurry-like composition, in which a powder of the active material is dispersed in a solvent (active material composition), forms a layer consisting mainly of the active material (active material layer) by applying to an electrode power collector. An aqueous active material composition, in which the solvent that composes the above-mentioned medium (dispersion medium of the active material powder and the like) is an aqueous solvent, is preferable for the active material composition used in this method from the viewpoints of, for example, reduced burden on the environment, reduced material consumption, simplification of equipment, reduced waste, and improved handling ease.
However, depending on the contents of the active material, problems can occur such as a decrease in battery capacity due to the use of an aqueous composition or a decrease in discharge characteristics due to an increase in initial internal resistance. These can be caused by a reaction between the active material contained in the paste and water. For example, in the case of using a lithium transition metal oxide such as a lithium-nickel-based oxide as a positive electrode active material (referring to an oxide containing lithium and one type or two or more types of a transition metal element as constituent metal elements, and to apply similarly hereinafter), an exchange reaction between protons and lithium ions can occur on the surface of the positive electrode active material dispersed in an aqueous solvent, thereby resulting in the pH of the aqueous active material composition being high (namely, becoming alkaline). When this high-pH aqueous active material composition is applied to a positive electrode power collector (such as an aluminum power collector), compounds demonstrating high electrical resistance (such as oxides or hydroxides) may easily form on the surface of the power collector. This formation of compounds having high electrical resistance can cause an increase in initial internal resistance of a battery (and eventually impair high output).
With respect to this point, Patent Document 1 describes a technology for providing a layer (conductive layer) containing an organic solvent-soluble polymer (binder) and an electrically conductive material on the surface of a power collector, and using this layer as a barrier layer that inhibits direct contact between water and the power collector to avoid a phenomenon by which the above-mentioned compounds having high electrical resistance are formed when forming an active material layer by applying an aqueous active material composition onto the layer.    Patent Document 1: Japanese Patent Application Laid-open No. 2006-4739